After searching for archives holding md5 files that were usable (see below) I ended up with the file, downloaded, checked hash and enabled firmware upload feature and started the upgrade. I also saw some message in the GUI after a while, about upgrade being in progress and that reboot would take place soon after.

After this I haven't been able to access the domain where the box is to be found. DynDNS is correctly configured on that box.

What can have happened. Why isn't my box online? What's your best guesses?

I have now travelled across town to manually re-boot the PC and yet I still can't access the webGUI remote when I return.There's was monitor available so I couldn't see if there's any errors prompted on boot.

No Ideas here, but since the upgrade failed, I hope you took the opportunity to do a clean install because while one or two or the earlier releases of 1.2.3 reflected such results, the current releases do not. Thus far, EVERY, upgrade has migrated the configuration correctly and continues to allow remote access on my end. However, I did have to do a clean install. Sometimes, you just have to call it "george" and start again.

It would be interesting to see some statistics on this, the likelihood of an upgrade failing, in general terms.

I do have a full backup of the config and that box has no packages installed either, I'll just try to load it after install then. But if I have to do this process every time an upgrade is available it's kinda time consuming. Let's hope it's a one timer then.

Also, if I'm not mistaken there's some way of having it picking up a config file during install, like from USB or something, I'll try find it through the search feature.

my upgrade failed as well. When I tried to connect to the webgui, it stated that an upgrade was in progress. The box was still functioning though, wireless/lan/internet/.... all worked. Three days later, the webgui still stated that the upgrade was in progress. I did then a reset of the box, after which it failed to boot.

I attached a monitor and looked at the box booting, but I couldn't really see anything in particular. It says something about not being able to load kernel and returns to some kind of command prompt saying "OK" to the left.

The image I used was ok and md5 checked ok.

I will not yet reinstall pfSense on that box (it now serves as an AskoziaPBX test install instead).